1. Field of the Invention
The present invention relates to reclosable plastic bags of the type in which food products, such as chips and cereal, and other goods are packaged for sale to consumers. More particularly, the present invention relates to reclosable plastic bags manufactured and filled on form-fill-seal (FFS) machines, wherein a series of interlocked plastic zipper strips are attached at bag-length intervals transversely to the longitudinal axis of the thermoplastic film material used to form the reclosable bags on the FFS machine.
2. Description of the Prior Art
The present invention relates to improvements in the package-making art and may be practiced in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture and air-tight packages, free from leakage until initially opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein. The prior art is fairly well-developed, but nevertheless remains susceptible to improvement contributing to increased efficiency and cost effectiveness.
One problem that persists with reclosable packages produced from a continuous supply of thermoplastic film material on FFS machines is the difficulty in attaining a satisfactory sealing of the bag or package against leakage, particularly where the zipper and area of film engaged by the zipper extends through the side (cross) seal areas separating one bag or package from the next. This problem occurs where the zipper is attached parallel to the longitudinal axis of the thermoplastic film material used to form the reclosable bags on the FFS machine, in which case the transverse, or side, sealing bars must flatten and seal the zipper at the same time they are sealing the thermoplastic film from which the packages are being made. The difficulty with which this is consistently and successfully achieved is reflected by the high occurrence of leaking packages.
In addition, the length of reclosable packages made on FFS machines wherein the zipper is attached parallel to the longitudinal axis of the thermoplastic film is limited to the diameter of the filling tube of the FFS machine. Thus, generally bags of this type are wider than they are long. While such bags are suitable for certain products where shorter bags are desirable, such as cheese and chicken parts, these bags are not suitable for applications in which longer bags are desirable, for example chips and other snack foods.
Among the approaches taken to solve these problems has been the substitution of a transverse zipper for the longitudinal zipper. A method and apparatus for making reclosable bag material and reclosable bags on a FFS machine utilizing transverse zippers is disclosed in U.S. Pat. No. 4,909,017.
When a transverse zipper is provided, the cross-sealing bars associated with the FFS machine do not flatten the zipper profile during formation of the top and bottom seals of the package since the transverse sealing bars may seal the zipper to the thermoplastic sheet material transversely thereacross without contacting the zipper profile. In addition, when a transverse zipper is used the length of the packages made on the FFS can be varied without varying the length of the transverse zipper segment and is not limited to the diameter of the filling tube.
The present invention relates to a method for attaching a transverse zipper to thermoplastic film material which is used to make reclosable plastic bags or packages on a FFS machine. More specifically, the present invention is a method for securing the zipper strip transversely across the thermoplastic film from which reclosable bags are produced on a FFS machine wherein the zipper strip is sealed to the film at the zipper strip's ends.
When attaching zipper strip to film material for use in transverse zipper applications with a process generally described in U.S. Pat. No. 4,909,017, it is critical that the leading edge of the zipper strip be sealed to the film before it enters the forming area of the FFS machine. If the leading edge of the zipper strip is not sealed to the film, then the zipper strip could become detached when in enters the tube area of the FFS machine. To overcome this problem, a webbed zipper having leading flanges of unequal width is typically used in transverse zipper applications. This disparity in web width makes it possible to seal the zipper strip to the film by sealing only the longer of the leading flanges to the film along its length. If the leading flanges were the same width and traditional sealing methods were used, then the flanges would be sealed to each other as well as the film, thereby sealing the zipper strip closed and making same unusable.
The problem with this current method, however, is that it requires manufacture of a special zipper strip having leading flanges of different widths, which is often difficult and expensive to manufacture. Thus, the object of the present invention is to provide a method wherein a zipper strip having equal leading flanges, or even no leading flanges at all, can be attached to the thermoplastic film material such that the transverse zipper-equipped film can be formed into reclosable bags or packages in the FFS machine.